Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August Calibration results of the first two H·E·S·S· telescopes Nicolas Leroy for the H·E·S·S· collaboration Muons Gamma-like

Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August Calibration coefficients To provide data analysis for physics we need on short time-scales: Conversion factor between ADC and photo-electron (p.e.) Correction of camera inhomogeneities Pedestal position and excluded pixels we also use muon images to monitor the detector and check our calibrations i.e., Classical Calibration

Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August Calibration of the detection system: atmosphere, mirror, Winston cones, PMTs, and electronics Atmosphere PMTs + electronic Winston cones + photocathodes Mirror Single p.e. calibration Laser calibration Muons Calibration coefficients

Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August Classical methods - Calibration runs ADC to photo-electron conversion factor using a LED system 80 ADC counts Width of electronic Pedestal: 0.18 p.e. Flat Fielding Using a UV laser or a pulsed LED at the centre of the mirror = 1 pe Fit with a sum of Gaussians ADC counts Run number ADC to pe Flat-Field coefficients 25 % Correction factor for each pixel uniform response of the camera Detection of a damaged pixel (excessive illumination)

Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August Crab Nebula field of view  Tauri Excluded Pixels HV Off HV unstable stars, highly-illuminated pixels Classical method - In data runs Pedestal position determined every minute in presence of Night Sky Background ~4 % of the pixels per run are excluded from the analysis High voltage current (  A) NSB (Hz) Night Sky Background determination using High Voltage Current information from the PMTs Analogue Ring Sampling chip not synchronised

Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August Cherenkov emission of a single particle Muons represent half of the trigger rate (~150Hz) in single-telescope trigger configuration Unique calibration tool providing information on the whole detection system with a real Cherenkov spectrum Validation of detector simulation Muons from hadronic showers are also very useful for calibration purposes

Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August : total collection efficiency : impact parameter : azimuth of the maximum in intensity : ring width : ring radius : ring centre in the camera Simple geometrical fit Geometry of Cherenkov emission from a muon ➢ complete ring in the camera (~1Hz) For each pixel, we determine from  i s the conversion factor between p.e. and photons Cherenkov emission is the Cherenkov angle, i.e., the ring radius in the camera falling in the mirror R X,Y x,y R e e q r s j max 200 nm < l < 700 nm e I( j ) % sin(2 q ).D( j ) e

Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August Reconstruction Radius (mrad) Total charge in the ring (pe) Intensity vs. Radius (real data) Simulations Data Between 200 nm and 700 nm Conversion factor between Photon and photo-electron CT3 07/2002 Conversion factor and MC Distribution for one run provides a good modelling of the detector in simulations

Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August Average conversion factor between 200 and 700 nm as a function of time Conversion factor ~ 4 % Flat Fielding with muons using fit residuals per pixel Distribution of average muon fit residuals Small shift in efficiency for CT3 Same behaviour between CT2 and CT3 Atmospheric effects ? Monitoring of the telescopes Average muon fit residuals for two pixels as a function of time good channel damaged channel e per run

Leroy Nicolas, HESS Calibration results, 28 th ICRC Tsukuba Japan, August Conclusions H·E·S·S· uses different independent methods of calibration Classical methods with LEDs and laser systems Muon ring images in data Allow a realistic calibration of our detector simulation Monitoring of each detector performance at the few percent level Accurate correction on flat-fielding Muons also provide information for selection of good-quality runs